Control system



Sept. 24, 1946. w ERNST 2,408,303

' I cONTROL SYSTEM Fil ed May 10, 1945 Ill/ll/l/l/I III/Ill INVENTOR WALTER ERNST,

BY vW ATTORNEYS Patented Sept. 24, 1946 UNITED STATES PATENT OFFICE l V I .2,-4os,s0s

I v V c n'rRoL SYSTEM Walter :Ernst, Mount; Gilead, Ohio, assignor. to

The Hydraulic Development Corporation, Inc Wilmington, Del.,, a corporation of Delaware Application'May 10, 1943, SerialNo. 486 ,1283:

' 4--Claims.

This invention relates to hydraulic systems andyin particular, to hydraulic control systems including a fluid-pressuresource of the variable delivery type.

I-t-is an object ofthis' invention to providea hydraulic system which includes areciprocable plunger and a pressure 'flui'dsourc'e of variable delivery for supplying; pressure-fluid to said plunger, and in which the-delivery of the pressure-fluid source -tosaid plunger 'is controll'edaue tomatica'l-ly response to the-resistance encountered-' by saidmotor. r 1 It' is anotherobj'ect' to=provide a hydraulic system including a fiuid operable 'plunger actuated by a pressure i-lu-id source of-variable delivery, in which a fluid flow "restriction is interposed between the-fluid sourceand the plunger, and in which the. delivery oil the fluid source is auto matically controlled so i as. -t'o=-hold the pressure drop across; said --restriction-- substantially constant during the working stroke of. said. plunger.

It is-a. further object to provide a hydraulic systenrincluding fa. pressure fluid Source-of." vari ableadelivery and-;.-a plunger operable by-fiu id from.-.said; fluidzsouree, in .which: a fiuid: fiovv restriction. isinterposediabetween, said; fluid. source and.;said plunger and .ishydraulically:wnn'ected with control plunger meansvarying the delivery of said fluid sourcein response to variations in the. pressuredrop acrosssaid restriction.

These andother obj ects and ad'v aritages inthe restriction will causethe control plunger to vary invention will appear-more-= clearly from the following; specification in connection with: -the ac= companying drawing, in which Figure 1 :diagrammatica1ly illustrates a 'hy- General arrangement The hydraulic: systemziaccord-ingitoathez. invens tion substantially. comprises azfluidxsource of;vari-.-.

able "delive 'mg uch. as a variable delivery pump...

and: a,-fluid; operable plungen while: a fluid; now restriction, such as a -.choke: valve, is; interposed between the, delivery; sideot; the fluid,- source and at least the advancing sidev ofythe, plunger tozhe controlled. The arrangement issuch vthat. the

delivery-; of the; fluid. sourceto; the ra'dvaneinggside of the. plunger must pass. through the. fluid flow 2. restriction. Both sides of the fluid flow restriction are connected with two opposed substantially equal areas of a 'fluid operable control plunger adapted whenmoving to vary the delivery'of the fluid source, Therefore, any'substantial variation in the pressure drop across the fluid, flow the delivery of said fiuidsource in such a manner that the initial pressure drop is-restored.

Structural arrangement" Referring novv tothe drawing. andto Figure-i thereof in. particular, the. system shown therein comprises a cylinder I having 'reciprocably mounted therein: a plunger 2 with an advancing area 3 and a retraction area 4, Connected to-one end of thecy-linder l is a conduit 5 comprising a preferably adjustable choke 6 and leading toa conduit 1. 'Oneend 0f the. conduit Iv communicates with a conduit-8 comprising alcheck Valve 9 and communicating-withtheconduit5;; 'Ilhe conduit 8 furthermore communicates with a four-way valve l 0 of anystandarddesign-adapt.- ed, whenin one. extreme position, to effect fluid communication between the pressure line :H I and the line 8 while simultaneously connecting the conduit. I2, communicating with the retraction side of the plunger 2, with-the-.exhaustylinelQ leading to a fluid-reservoir or tank [4; When the valvefllroccupies its other extreme position fluid communication is established between themes:- sure-z line H and the conduit t2, while-simultaneously the conduit: I3 is connected with .the con duit 8. When the. valve t0 occupies-its intermediate or center position, no fluid passes; through the valve. The check valve 9 in the conduit fl-isso arranged as to permit thefiow oifiu-id-th rethrough: from the. conduit 5 to the-four-way: valve l0, while preventing: the flowof fluid in the reverse direction.

The.conduit.|-'1eads/to a control cylinder. l5 having-reciprocably mountedrtherein a plungenlfi' of substantially equalopposed areas l1 and-xiii. The'plungery I6 is connected to the .fiow control member of a variable delivery. pump: |9 sotliat rightward movement of the plunger l6:with regard to Figure. 1 decrease; the delivery of. the

pump l9, whereas leftward movement of the. plunger I6 causes a spring 20in the springxchamber 2| to act upon the flow control member of the pump. l9 sons to increase the deliveryof the pump Hi. The spring. 20,, which continuously urges the pump l9 into full delivery position, isadjustable with regard to its thrustby meansof an adjustingscrew. 22, The-spring chamber 2| ga ses 3 is hydraulically connected through a conduit 23 with the fluid tank I4. The fluid tank furthermore communicates through a conduit 25 with the suction side of the pump I9 and also cornmunicates through a conduit 25 with a bore 2% in an extension of the control cylinder I5. This bore serves for guiding the control plunger I6. The area I8 of the control plunger I6 is hydrau lically connected through a conduit 2'! with the conduit 5.

Opposition It may be assumed that all parts of thesystem shown in Figure l occupy the position in which they appear in the said figure. If it is now desired to have the plunger 2 perform a working cycle, the operator shifts the valve In into position for establishing fluid connection between the pressure line II and the conduit 8 while simul. taneously connecting the v conduits I2 and I3 with each other. Provided the pump I9 has been started, pressure fluid delivered by the-pump I9 will now pass through line II, valve I9, conduits 8, I and 6. From there the pressure fluid will pass through conduit 5 into the left hand position of the cylinder]. Here it will act upon the advancing area 3 of the plunger 2 and move the latter rightwardly. The fluid expelled by the plunger 2 from the cylinder I during this rightward movement escapes through the conduit I2, the valve I I and the conduit I3 into the tank I4.

When the fluid delivered by the pump I9 passes throughthe-choke valve 6, a pressure drop will occur across this choke valvewhich pressure drop will make itself felt on the opposed areas IT and I8 of the control plunger I6. Since the pressure in the conduit I and therefore on the areas I? of plunger I6 Will be greater than thepressure in the-conduit 21, and therefore uponthearea I8, the pressure acting on the area I7 Will some- What counteract the spring 20 and slightly reduce the delivery of the pump I9 until the pressure acting on the area I! balances the pressure acting on the area I 8 plus the thrust of the spring 2EI. When this balancing position has been reachedjthe flow through the-choke valve 6 and thereby the pressure drop created thereby will under normal conditions remain substantially constant, and the plunger 2 will perform its working stroke at a substantially constant speed.

If it should not occur that, for some reason,-the plunger 2 encounters increased resistance, this will temporarily slow down the movement of the plunger 2. As a result thereof the pressure in'the lefthand portion of the cylinder I and therefore, also in the conduit 27 will increase to a greater extent than the pressure in the conduit '1'. Consequently the previously mentioned balancing condition will be disturbed, and the plunger it will be moved leftwardly until the pressure acting upon the area I'l' will again be balanced-by the pressure acting on the area I8 plus the thrust of the spring 20. In view of the thus efiected left- Ward movement of theplunger E6, the spring 253 acts upon the control member of thepump ISso as to increase the delivery of the pumpis. in view of this increase in the delivery of the pump I9, the previous flow across the choke 6 will be restored and therefore also the previous pressure drop across the choke .6. The plunger 2 will consequently resume its previous speed. The control plunger I6 will maintain its new position, i. e., the thus changed delivery of the pump I9 will now be maintained as long as the resistance encountered by the plunger 2 .remainsthe same.

If it should occur that, for some; reason, the

'- the pump I9 so that the previous flow across the 4 resistance encountered by the plunger 2 during its advancing movement drops, the plunger 2 will tend to increase its advancing speed. As a result thereof the pressure in the conduit 21 will drop to a greater extent than the pressure'in the conduit 1 so that the pressure acting upon the area U will overcome the pressure acting upon the' area I8 plus the thrust of the spring 20, and will move the plunger I6 right'wardly; This control will result in a decrease in the delivery of choke 6 and thereby the pressure drop across the choke will be restored. Therefore the plunger 2 will again move' at its initial speed, and the control plunger I6 will maintain its position as long as no'further variation in the resistance encountered by the plunger 2 occurs.

When the plunger has reached the end of its working stroke, and it is now desired to reverse the plunger 2, the operator shifts the valve In into position for establishing fluid connection between the pressure line II and the conduit I2, while simultaneously connecting theconduitst and I3 with each other. Pressure fluid deliveredby the pump I9 now passes through conduits II and. I2 into the right hand portion of the cylinder I. Here it acts upon the retraction area 4 of plunger 2, thereby causing the plunger 2 tomove leftwardly. The fluid expelled from the left hand portion of the cylinder I duringthis leftward movement of the plunger 2 escapes through the conduit 5, check valve 9 and conduits .8 and I3 into the tank I4. It will be noticed that during this retraction stroke the choke 6, is by-passed and therefore is ineffective, so that no speed control is exerted upon the plunger 2 duringits re: traction stroke. However, in general, no speed control is necessary during the retraction stroke of the plunger 2 since, as a rule, no variations in resistance occur during the retraction stroke-of the plunger 2. e

. When it is desired to brin flthe plunger 2 to a stop, the valve. I0 is moved-into its neutral position and the pump I9 is either stalled or standard servomotor means, which maybe associated with the pump. I9, will cause the pump l9 to shift into substantially neutral or no delivery position.

Second embodiment Referring now to Figure 2, the structure shown therein substantially corresponds to the structure of Figure 1 withzthe exception that additiona1 control means are provided for efiecting a speed control also during .the retractionstroke of the plunger. .To'more clearly indicate v.the

similarity. between Figures 1 and 2, the elements of Figure 2 corresponding to those of Figure 1 have been designated with the same reference numerals as inFigure 1 however, with the additional character-a. The difference between thestructure of Figure 2 and the structure of Figure 1 consists in that the control mechanism associ-- ated with the advancing side of the plunger 2a is duplicated for the retraction area do. To this I end the righthand portion of the cylinder la is connected with a conduit 28 comprisinga choke 2a and leading to the four-way valve Hid; Branching off from the conduit 28-is a conduit 30 containing a check valve 3| adapted to-allow the flow of fluid therethrough fromith e'right hand portion of the cylinder Ia to the check valve Illa while preventing the-flow of fluid in the opposite direction. Also branching on from the conduit 28 is a'concluit 32 leadingto the control-cylinder 33. The control cylinder 33 has -re-' s ciprocablyi mountedtherein a plunger .34 with two" opposed substantially -equal area 35- andL36.

The area -35 is engaged bya spring- 20a =continu-.

The control of the plunger 2a during its ad- I vancing movement fully corresponds to the control of the plunger 2 during the advancing movement thereof, and therefore the description of the advancing movement of the plunger 2a appears to be superfluous. However, as previously mentioned, in the arrangement of Figure 2 also the retraction stroke of the plunger 2a will be controlled as to its speed.

It may be assumed that the valve Ilia occupies the position in which the pressure line Ila is in fluid communication withthe conduit 28 while simultaneously the conduitla communicates with the conduit I3a. Pressure fluid will then be delivered by the pump 19a through the choke 29 into the right hand portion of the cylinder la, thereby causing the 'plunger 2a to move leftwardly. The fluid expelled from the left hand portion of the cylinder la escapes through the check valve 9a, the conduit la and the conduit l3a into the tank l4a. If now, for some reason, the resistance encountered by the plunger 2 during its retraction stroke should change, the pressure drop across the choke 29 will also change so that the pressure conditions in the control' cylinder 33 will vary accordingly. As a result thereof, the plunger 34 will be moved in a manner similar to that described above in connection with the plunger I6, and will bring about a corresponding change in the delivery of the pump l9a. Therefore, the initial flow of fluid across the choke 29, and thereby also the original pressure drop across this choke will be restored and the plunger 2 will be moved at substantially its original speed.

It will be obvious that by varying the setting of the chokes 6, 6a and 29 the desired speed of the plungers 2 and 2a may be varied. It will also be clear that by setting the chokes 6a and 29 differently the advancing speed and the retracting speed of the plunger 2 may be independently controlled.

" Third embodiment The system shown in Figure 3 makes use of the same principle illustrated in Figures 1 and 2 and similar parts are designated by the same numerals as in Figure 1, but with the additional character 0. However, in Figure 3 the plunger 40 to be controlled has a piston portion 4| with substantially equal areas 42 and 43. Furthermore, the position of the four-way valve I and the choke 60 has been reversed with regard to the pump 190. In other words, the delivery of the pump [9a to either the area 42 or the area 43 must always pass through the choke 6a so that the advancing as well as the retraction stroke of the plunger 40 is controlled. However, the set ting of the choke Ba will equally affect the control of the plunger 40 in its advancing and retracting directions. Otherwise, the operation of the system shown in Figure 3 fully corresponds tothat of Figures 1 and 2' so thatnofurther description thereof appears necessary;

It will be understood that.. the present ins/em tion. is by no. means limited to. the particular structureshown inthe drawing, but alsoembraces any. modification falling within. the; scope of. the

appendedclaims.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent, is: g

1. In a hydraulic system, the combination with a variable delivery source of pressure fluid, of a reversible fluid motor having a pair of ports and operable in both directions by fluid supplied to said ports from said source, a first flow restricting means hydraulically connecting said source with one of said ports, a second flow restricting means connecting said source with the other of said ports, conduit means adapted freely to exhaust either of said ports when the other is being supplied with pressure fluid from said source, yielding means for continuously urging said fluid source toward maximum delivery position, a first and a second double acting plunger each having two opposed and substantially equal areas thereon respectively connected with the inlet and the outlet of said first and second flow restricting means respectively, said plungers being connected to vary the delivery of said fluid source.

2. In a hydraulic system, in combination with a variable delivery source of fluid and a reversible fluid operable motor having a pair of ports and operable in both directions by fluid supplied to said ports by said source, a first adjustable choke valve connecting said source with one of said ports, a second adjustable choke valve connecting said source with the other of said ports, conduit means associated with said ports and adapted freely to exhaust one of said ports when the other is being supplied with actuating fluid, yielding means continuously urging said source toward maximum delivery position, a first and a second double acting plunger each having two substantially equal opposed areas thereon, said first and second plungers having their opposed areas respectively connected with the inlet and the outlet of said first and second choke valves respectively, said plungers being connected to vary the 50 delivery of said fluid source.

3. In a hydraulic system, a reversible fluid operable motor having a pair of ports, a variable delivery source of pressure fluid for selectively supplying actuating fluid to said ports, means 55 for connecting said source with one of said ports including a first adjustable restriction, means connecting said source with the other of said ports and including a second adjustable restriction, a first and a second check valve bypassing said first and second restriction respectively, each of said check valves being adapted to conduct fluid away from said motor but not vice-versa, adjustable yielding means for continuously urging said fluid source toward maximum delivery 5 position, a first and a second double acting plunger having twosubstantially equal opposed areas thereon associated with said source and connected to vary the delivery thereof, said first and said second plungers each having the opposed 70 areas thereof respectively connected with the inlet and the outlet of said first and second flow restrictions respectively.

4. In a hydraulic system, in combination with a fluid source of variable delivery, a reversible 75 fluid motor having a first and a second port, first and second flow restricting means connecting said source with said first and second ports respectively and each operable to establish a predetermined pressure difierence between its inlet and outlet in response to fluid flow toward the associated port but to permit free flow from the said port, yielding means continuously urging 

